The long-term goals of this project are to define the role and regulation of sphingosine kinase 1 (SK1), an important enzyme in cancer, as a novel and critical downstream target for serine deprivation, and to establish a novel non-canonical pathway of bioactive sphingolipids and SK1 as a potential serine sensor and effector mechanism, critical for metabolic reprogramming. Although serine is a non-essential amino acid, rapidly proliferating cancer cells also need an exogenous source of serine for optimal growth. Importantly, serine is a direct precursor of sphingolipids which are synthesized by the condensation of serine and palmitoyl Co-A by the enzyme serine palmitoyl transferase (SPT). Intriguingly, this enzyme can also utilize alanine as a substrate, especially in the context of relative serine deprivation, and this generates the novel, non-canonical, sphingolipid 1-deoxysphinganine (dSa). In very recent and exciting preliminary studies, we find that serine deprivation drives the accumulation of dSa, which in turn induces loss of SK1, which then launches pathways of metabolic reprogramming and adaptation to serine deprivation. These studies raise a number of fundamental questions as to the specific mechanisms of serine deprivation on SK1 regulation, the effects of serine deprivation on the networks of bioactive sphingolipids: which specific bioactive lipid mediates what specific serine deprivation responses, and what are the biologic consequences and mechanisms involved? To address these questions we propose the hypothesis that serine deprivation leads to SK1 loss in a novel mechanism involving the generation of dSa. The resultant accumulation of the SK substrate sphingosine regulates adaptive downstream biologic responses and metabolic reprogramming pathways. This hypothesis and its corollaries will be investigated by pursuing the following specific aims: Specific aim 1. To define the mechanisms by which serine deprivation induces SK1 loss. Specific Aim 2. To determine the biologic functions mediated by SK1 loss in response to serine deprivation. Specific Aim 3. To determine the role of SK1 loss in the metabolic reprogramming of cancer cells in response to serine deprivation and the mechanisms involved. Identifying the mechanisms by which serine deprivation regulates SK1 and bioactive sphingolipids will not only shed light on these exciting novel connections between these two metabolic pathways, but will also result in the identification of novel therapeutic targets.